Enteric Gram-neg (part 1) Flashcards
ENTEROBACTERIACEAE
What is the medical importance of the enteric family?
Indicator of fecal pollution of water
30% of hospital acquired cases (nosocomial infection)
Easily studied genetically
Difficult to treat with antibiotics
Physical characteristics of Enterobacteriaceae
Gram-neg, medium sized rods
Flagella if mobile
Non spore forming anaerobes
What are some non-motile Enterobacteriaceae?
Klebsiella and Shigella genus
Cultural characteristics of Enterobacteriaceae
Ferment glucose
Resistant to acid and bile
What makes Enterobacteriaceae toxic?
Lipid A
Lipid A + O polysaccs=Lipopolysaccharide (endotoxins) –> on their cell wall
Selective media used for Enterobacteriaceae
Unioculated MacConkey
Which Enterobacteriaceae are lactose fermenters?
E. coli, Klebsiella, Enterobacter
with a pink pigmentation
Which Enterobacteriaceae are non-fermeters?
Salmonella, Shigella
with straw colored colonies
What are gram inhibitors?
Dye crystal violet that suppresses unwanted Gram-pos organisms by bile salt or bacteriostatic dye
Triple Sugar Iron (TSI)
Indicator media
Tests organisms for carb fermentation, gas production, hydrogen sulfide production
How do you categorize TSI?
Black= H2S
Cracks= Gas
Red slant= glucose used (no lactose and peptones used)
Yellow= all sugars fermented
How is salmonella and proteus classified by the TSI?
Slant= alkaline (red)
Butt= acid (yellow)
Gas (cracks) and H2S (black) positive
How is Enterobacteriaceae divided?
- Major pathogens
- Opportunistic pathogens
- Organisms of uncertain significance
Major pathogens
Salmonella
E. coli
3 Yersinia species
Opportunistic pathogens
Klebsiella, Enterobacter, Proteus, Edwardsiella, Citrobacter, Morganella, Shigella
There are over ______ genera and over ______ species
40
180
Escherichia coli (E. coli)
Ferments lactose
165 O chains, 50 H (flagella), 90 K (capsules) strains = over 1000 strains
Habitat of E. coli
Large and small intestine of mammals
Excreted in feces and can survive in dust, water and fecal particles for months
E. coli in water= fecal pollution
Adhesions
Fimbira/pili
Mediate adherence to the target cells (glycoprotein) in the GI tract
Capsules
Protects E. coli from complement cascade and inhibits microbe from attaching to phagocytic cells
What enterotoxins does E. coli produce
Heat liable toxin (LT)
Heat stable (STa and b)
Entero-aggregative heat stable (EAST 1)
How do enterotoxins affect cells?
Affect control of cyclic nucleotide activity within the affected cell –> deregulation of water and electrocytes
Predisposing causes of E. coli
Neonates obtaining insufficient Abs from colostrum
Intensive husbandry system
Poor hygiene
Stress factors